This invention relates to an aluminum alloy suitable for use in fabricating an electrical conductor and more particularly concerns an aluminum alloy suitable for fabricating an electrical conductor for use in applications in which the electrical conductor is required to have high tensile strength and to retain tensile strength for extended periods of time at high operating temperatures.
The use of various aluminum alloys to fabricate electrical conductors is well established in the art. Such alloys characteristically have conductivities of at least 61 percent of the International Annealed Copper Standard, hereinafter referred to as IACS and chemical constituents consisting of a substantial amount of pure aluminum and small amounts of impurities such as silicon, vanadium, iron, copper, manganese, magnesium, zinc, boron and titanium. The physical properties of electrical conductors fabricated from prior aluminum alloys have proven less than satisfactory for many applications which reqire that the electrical conductor used have a high tensile strength which is retained after extended periods at high operating temperatures. Generally desirable tensile strength and thermal stability have been obtainable only at less than desirable elongation.
For example, it is generally accepted that industrial purity aluminum has a recrystallization temperature of from about 300.degree. to about 662.degree.F (150.degree. to 350.degree.C). It is also accepted that such aluminum has a very low resistance to heat and undergoes a softening phenomenon at a temperature of from about 212.degree. to about 392.degree.F (100.degree. to 200.degree.C). Much work has been done in the past to improve the heat resistance of aluminum, however the majority of alloys developed which have acceptable electrical conductivity undergo a significant loss of strength upon being exposed to temperatures of from about 300.degree. to about 392.degree.F (150.degree. to 200.degree.C) for several hours. Such alloys usually retain only from about 60 to about 80 percent of their original tensile strength and elongation after exposure to temperatures in this range for several hours.
Thus, it becomes apparent that a need has arisen within the electrical industry for an aluminum alloy from which electrical conductors might be fabricated which will have improved thermal stability, tensile strength and elongation and acceptable conductivity, and yield strength.
In the past aluminum alloys and rod for the fabrication of wire have been manufactured for commercial use by a plurality of separate steps which include casting an aluminum alloy ingot, reheating the ingot to a temperature which would permit hot rolling of the cast ingot into redraw rod, solutionizing the rod and water quenching the rod before cold drawing the rod into wire. After drawing the wire fabricated by the aforementioned procedure is generaly annealed in order to obtain acceptable tensile strength. Although wire produced by the aforementioned techniques has acceptable tensile strength, it is difficult and in fact almost impossible to produce an aluminum alloy wire having high thermal stability and acceptable elongation and electrical conductivity using this technique because the procedure inherently produces a structure which contains elements in solution because all the alloying elements are not removed from solution by the quenching steps and because large precipitates are formed if the alloy is processed at high temperatures. The cell structure of aluminum alloy wire fabricated from base metal so processed is unstable thereby promoting the formation of large cells when the wire is subjected to any heat treatment thereby leading to a finished product which has either poor thermal stability or poor physical and poor electrical properties.
Therefore it becomes apparent that there remains a need within the electrical industry for an efficient and economical method of fabricating an aluminum alloy and an aluminum alloy rod from which an electrical conductor having high tensile strength which is retained during extended periods at high temperatures and acceptable electrical properties can be fabricated.